visibility of class member in PHP5

The visibility of a member property or method of a class can be defined by prefixing the declaration with the keywords: public, protected or private. Public declared items can be accessed everywhere. Protected limits access to inherited and parent classes (and to the class that defines the item). Private limits visibility only to the class that defines the item.

Parent and child class can have a private set of private variables that no-one else has access to, other than the class itself even it was inherited. Which means private members of a class can’t be overridden.